Aneurysmal subarachnoid hemorrhage (SAH) remains a major cause of morbidity and mortality. Since the incidence peaks in mid-life, and since many survivors are permanently damaged, the human and economic costs are immense. Much of the death and disability is the acute and delayed result of blood in the subarachnoid space (e.g. vasospasm). However, an unknown - but we believe substantial - fraction of the adverse outcomes are a complication of surgery performed to obliterate the source of bleeding; as many as 25 percent of patients who undergo craniotomy for aneurysm clipping will have a new neurologic deficit when examined 12-24hrs postoperatively. This danger is well known, and almost all surgical teams utilize some method to protect patients during surgery, including barbiturates, etomidate, steroids, mannitol or varying degrees of hypothermia. Unfortunately, in spite of the popularity of such interventions, none has ever been systematically tested in humans (other than deep hypothermia and circulatory arrest), and none are known to provide any benefit at all. Of the aforementioned therapies, we believe the best laboratory evidence supports the use of hypothermia. Our goal, therefore, is to perform a prospective, randomized clinical trial to evaluate the safety and efficacy of intraoperative hypothermia (t=33 degrees C) as a means of reducing early and long-term postoperative neurologic morbidity following surgery for clipping of intracranial aneurysm. Control patients will remain normothermic during and after surgery; in hypothermic patients, body temperature will be normalized as quickly as possible after the aneurysm clip is in place. All other aspects of pre- and postoperative care will be managed routinely. We hypothesize that hypothermia, even when limited to the intraoperative period, will result in an improvement in neurologic outcome as measured by Glasgow Outcome Scale at 3months following surgery, and will also result in more rapid improvement during the first postoperative week.